Electronic motor control system



Nov. 23, 1948. H. NYGAARD ELECTRONIC MOTOR CONTROL SYSTEM 2 Shouts-Sheet 1 Filed Feb. 12, 1945 r o- ELECTRONICo- CIRCUIT :1: CONTROL I INVENTOR. HERMAN NYG/MHO A .A TTORNEY Nov. 23, 1948. H. NYGAARD 2,454,401

ELECTRONIC ROTOR CONTROL SYSTEM Filed Feb. 12, 1945 z sheets-sheet 2 I A57 I ATTORNEY Patented Nov. 23, 1948 ELECTRONIC MOTOR CONTROL SYSTEM Herman Nygaard, East Orange, N. .L, assignor, by mesne assignments, to Lear, Incorporated, Grand Rapids, Mich., a corporation of Illinois Application February 12, 1945, Serial No. 577,426

20 Claims. 1

This invention relates to electronic motor control systems, and more particularly to such systems including electronic control means for stably following up the movement of a position selector.

The system of the present invention is particularly applicable to the remote control of the position of movable accessories on aircraft, for instance throttle controls, wing flaps, cowl flaps, landing gears, intercooler shutters, propeller speed governors, etc. On the larger aircraft, such mov-- able accessories are usually positioned by means of power driven linear actuators, the operation of which is remotely controlled from a position adjacent the pilots compartment. The present invention provides presettable positioning or follow up control of the driven member throughout its positionable range.

Electrical motor drive systems are replacing the more bulky hydraulic systems in many instances on aircraft. The present invention provides continuous remote positioning control of the available motors on aircraft actuators, whether operated from a low voltage direct current or higher voltage 400 cycle source. To save excessive drain on the power source, the control system is designed so that the power is used by the actuator motors only during their actual operating periods. Furthermore, there is a wide variety in the sizes and types of drive motors used aboard a modern aircraft. Under certain conditions, the use of direct current motors may be indicated; and under other conditions, alternating current motors. Each motor must be particularly designed for its particular application on an aircraft, taking into consideration the type of power economically available thereon, the load, and other conditions.

The principles of the present invention are applicable to any type or size of motor to be controlled, afiording smooth and rapid operation of the controlled member, accurately to its new positions. The pilot need merely turn a dial to the required indicated position, and the motor is controlled to effect that new position of the member. No stand-by or other current is required to flow through the motor during nonoperating conditions. Thus no power is wasted, nor is the motor ambient temperature raised. This feature is essentially provided through the use of a relay control of the motor, as will be set forth hereinafter.

Another important feature is the provision of novel effective anti-hunt or stability characteristics inthe motor control system. In accordance with the invention, a signal or electrical 2 eflect produced as a result of the operation of the position selector, per se, is combined with the positioning or input signal to the electronic control means. This effects an anticipation for the control of the final position, and eliminates hunting in the drive system. Also, an electromagnetic clutch and brake unit is interposed between the motor and the actuator that abruptly disconnects the motor from the actuator as it approaches the final position, and also rapidly arrests motion of the actuator and driven member. Successive energization and deenergization of the clutch, brake and motor is afforded by the anticipation control to effect a stepping or chattering-in of the member to its final position. The clutch and brake unit-is particularly effective in small, or "inching movements as it disconnects the motor from the actuator and abruptly stops the latter. This further stabilizes the control system and can be made to effect rapid control movements on the member without hunting. Such stabilizinganticipation means is effective particularly for the relay controller for the motor, and renders such controller practical and feasible, particularly on aircraft.

It is among the objects of the present invention to provide an improved manual or automatic remote positioning control system including electronic follow-up means; to provide such a system which will insure rapid accurate positioning of a movable member driven by an electric motor; to provide such a control system having a narrow dead or back-lash zone, while, at the same time, having maximum sensitivity to small displacements of theposition selector; to provide such a system which is universally applicable irrespective of the type and size of motor to which it is applied or of the type of motor power supply available; to provide such a system in which a signal derived in response to operation of the position selector is combined with the input signal to insure stability and anti-hunt characteristics in the system; to provide such a system including means for disconnecting the driving motor fromthe actuator and abruptly stopping the latter when the positionable accessory is in coincidence with the position selector; to provide such a system in which no stand-by current is required for the drive motor; and to provide such a system which includes relatively few parts and is light in weight, simple and reliable in operation for all types of aircraft or flight conditions.

These and other objects, advantages and features of the invention will be apparent from the used in the invention control system.

Fig. 4 is a schematic wiring diagram illustrating another embodiment oi the electronic control circuit.

Fig. 5 is a schematic wg agrain illustrating still another embodiment of the electronic circuit.

Fig. 6 is a longitudinal sectional view through an electromagnetic clutch and brake t used in the control system.

Generally speaking, the system oi the present invention comprises a position selector operatively connected to a signal transmitter. The selector is effective to preselect the position of a movable member that is positioned by an actuator driven by an electric motor. A signal receiver is operatively associated with the actuator or the movable member, and electronic control means is provided connecting the signal receiver and signal transmitter. The control means is operative, upon receipt of an input signal due to angular disparity between the position selector and the movable member, to selectively operate relay means to energize the actuator motor for operation in the direction to restore coincidence between the position selector and the movable mem= her. When the movable member attains coincidence with the position selector, the electronic control means operates to deenergize the relay means to disconnect the motor from its source.

.To avoid hunting oi the movable member on either side of such coincident position, a counter signal responsive to operation or the position selector is combined with the input signal to effect accurate stopping of the actuator at such coincident position. The anti-hunt characteristics of the system are further improved by the use of an electromagnetic clutch and brake unit between the motor and actuator which operate to substantially instantaneously stop the actuator upon deenergization of the motor, afiording accurate control in small or inching movements of the movable member.

Referring to the drawings, the system-illustrated in Fig. 1 includes a position selector ill operatively connected to a position signal transmitter ii. The position selector is arranged to control the position oi a movable member which may, for instance, be a wing flap of an aircraft. Movable member 20 is power operated by means oi an actuator unit 25, which may be of the type described and claimed in copending application Serial No. 483,515 filed April 17, 3.943 by William P. Lear for Unitary mechanical actuator device, and assigned to the same assignee as this case. As described in said copending application, ac tuator unit includes a motor as connected through an electromagnetic clutch and brake unit I! and gear train to a jack screw 45. A control box 50 is included in the actuator assembly and contains limit switches, and in the present a case, a position signal receiver 55. A multi-cona junction box l2, which, in turn, is connected by multl-conductor cables l3 and I4 to control box 50 of actuator unit 26 and electronic control circuit unit 60. Leads l6 connect unit 80 to a source 5 oi alternating current and leads i-l connect the unit to a source of direct current.

Fig. 2 is a schematic showing of the components oi Fig. 1. The transmitter I5 and receiver 65 are shown as "Belsyn" units includi g multi-phase l0 stator windings 2| and 22, respect vely, and rotor windings 23 and 24, respectively. Transmitter rotor winding 23 is adapted to be angularly displaced within stator windings 2i, relative to receiver rotor winding 24, by a shaft 26 which is connected to selector in, which may include a knob 27 having a pointer 28 adapted tocooperate with indicia 8!.

A source of alternating current is connected to rotor winding 23 through leads 32. Due tothe 20 transformer action between rotor winding 23 and stator windings 2|, multi-phase sinusoidal alternating fields are set up in stator windings 2i. Leads 33 symmetrically interconnect stator windings 2| and 22 so that sinusoidal fields, corre- 25 spending in space and time relation with those in stator windings 2|, are set up in stator windings 22 of unit 55. When rotor windings 23 and 24 have a relative angular displacement of 90 electrical degreeswithin their respective stator windings, no voltage is induced in receiver rotor winding 24. Such 90 degree relation is hereinafter referred to as the "n position of the rotor windings.

. When transmitter rotor winding 22 is angularly displaced from null relative to rotor winding 24,

as through animation of knob 21 to preselect a new position for member 20, an output voltage is induced in rotor winding 24. Leads 34 from winding 24 introduce this output voltage as an 0 input signal or control voltage to electronic control circuit 80.

The magnitude of the resultant control voltage is proportional to the sine oi the relative angle of displacement from null; and the phue of this control voltage is in-phase or 180 out-of-phase with the reference or source input to winding 23, dependent on the sense of the angular displacement. The control signal eflects operation of the control circuits in unit 80 to effect selective connection of motor 30 to its source of power as will be described.

Motor 30 is connected to its source of power over a circult'which includes an energizing winding for electromagnetic clutch and brake unit 35 in circuit connection with the motor. For this purpose, where a series motor is used, one terminal of unit 35 is connected to unit Ell through lead 36, and the other terminal is connected to motor 30 through lead 31. The other two termico nals of motor 30 are connected through loads 38 and 4| to terminals of limit switches 42 and 43. Leads 44 and 46 connect the other terminals of limit switches 42'and 43 to control unit 60. Energizatlon of motor 30 and clutch and brake unit 35 connects motor 30 to a drive pinion H. Drive pinion 41 operates jack screw 45 through a system of pinions and spur gears indicated generally at 48.

Gearing 48 causes jack screw 45 and member 7 20 to be operated at its proper reduced rate of speed with respect to motor 30. As described in said copending application Serial No. 485,515, jack screw 45 includes a screw member 5| having threaded engagement with a sleeve member 52.

ductor cable ll connects signal transmitter i5 i0 Relative rotation of jack members 5! and 52 eflects extension and retraction of the jack screw to operate member 20. A spur gear 53 driven by a pinion 54, operates a shaft 56 connected to rotor 24 of unit 55. A worm 51 meshes with a worm gear 58 operating a pair of cams 6i and 82 which in turn cooperate with limit switches 42 and 43. Switches 42 and 43 may be so set that cams 5i and 82 will eflect opening of the motor circuit when member or lack screw 45 has mechanically reached its limit of operation in either direction.

As explained above, when there is a relative angular diflerence from the null or 90 degree relation in the position of rotor windings 23 and 24, a voltage is induced in rotor winding 24 proportional to the relative phase displacement of windings 23 and 24 from null relation within their respective stator windings. The voltage thus induced in winding 24 is applied through leads 34 to control unit 60 where, through connections to be described, it effects actuation of a differential relay for connecting motor and clutch-brake unit to a source of power for operation in a direction to restore coincidence between selector l0 and member 20. Unit 35 couples motor 30 to drive Jack screw through pinion 41 and searing 48. At the same time, gear 53 and shaft 56 rotate receiver rotor windin 24 in correspondence with the movement of movable member 20.

When member 20 has reached the position corresponding to that indicated by pointer 28 of knob 21, receiver rotor winding 24 is geared to be in 90 degree or null phase relation with rotor winding 23. When rotor winding 24 is thus angularly related to rotor winding 23, the output or control signal voltage across its terminals will have decreased in value to zero. Hence, there will be no signal input through leads 34 to unit 60. The effect of the rotor windings reaching a null signal position is to deenergize motor 30 and clutch 35 effecting substantially instantaneous stopping of movable member 20 due to the braking action of unit 35 on actuator 25. Due to gearing 48, 53 and 54, rotor winding 24 is moved at a greatly reduced rate with respect to the rate of rotation of the armature of motor 30. To avoid any ambiguity oi" positioning, position transmitter rotor 23, and therefore position re- 'ceiver rotor 24, designed to move in correspondence therewith, are not displaced more than 180 from null for the full range of control movement on member 20.

An important feature of the invention is the selective impressing of a counter or anticipa- 'tory signal upon electronic control unit 60 corresponsing to theamount and time of relative displacement from null of position selector I 0 with respect to movable member 20. Such counter signal is combined in control unit 60 with the control signal from receiver in a selective manner, dependent upon the direction of relative displacement of selector ID with respect to movable member 20. The effect of the counter signal is to reduce the effective value of the control signal applied through leads 34 to unit and effect deenergization of motor 30 somewhat before member 20 attains coincidence with selector 10. As will be made clear hereinafter, this effects a "stepping-in or chattering-in" of member 20 to the null or final position, inhibiting overshooting or hunting. By such null position is meant a substantially coincident phase or relation of the movable member and the selector in which the efl'ective value of the signal voltage impressed from receiver 55 on control unit is insufiicient to effect operation of motor 23.

With the systems of the present invention, such null zone is shifted in the direction oi relative dispacement of selector I 0 and movable member 20 to eflect deenergization of motor 30 before the movable member and the selector have been returned to a substantially coincident position. Such shifting of the null zone also sensitively conditions the electronic control unit for operation of the motor 'in the opposite direction in the event movable member 20 overrides the coincident relation with selector ID in a direction opposite to that oi. the original displacement. The shifting of the null zone renders the control unit extremely sensitive, in such event, to immediately restore movable member 20 to such coincident relation with selector i0.

In accordance with the present invention, the selective impressing of counter signals upon electronic control unit 60 occurs both as a result of the relative displacement of selector III with respect to member 20 and in response to energlzation of motor 30 due to such relative displacement. The

' counter signal responsive to the relative amount and time of displacement of selector III with respect to member 20 is effective for relatively large displacements. The counter signal means operative in response to energization of the motor 30 as a result of such relative displacement is particularly effective in relatively small displacements of selector ID with respect to movable member 20. In a preferred embodiment of the invention, both methods of anticipation are employed simultaneously to make the system suitably sensitive for both relatively small and relatively large displacements of the selector with respect to the movable member.

Fig. 3 illustrates one embodiment of a control and anti-hunt arrangement for motor 30 as included in unit 60. In accordance with the invention, motor 30 may be a direct current series motor comprising an armature 65 and reverseiy wound field windings 66 and 61. One motor armature terminal is connected to one terminal of a source of direct. current} such as a low voltage aircraft battery or generator Iii, which may be the same as that represented by conductors il in Fig. 1. The other motor armature terminal is connected to a junction point 5% oil fleldwindings 66 and 61. The outer terminals of the field windings are connected respectively' to front contacts H and 12 associated with relay operating coils 13 and (4. Relay armature sections 15 and 18 are shown commonly connected .to the other terminal of source 'lll through junction point Ti.

While relay coils l3 and 14 have been shown as separate relays in Fig. 3, and also in Figs. 4 and 5, this is merely for convenience and clarity of'illustration. Both coils are part ofa single 'diflerential relay 19, such as shown schematically in Fig. 3A. This differential relay includes oper ating coils 13 and 14, a pivoted armature 88 including armature sections 15 and 16, and front contacts 1| and 12, each operatively associated with one armature section. Pivoted armature 89 is indicated in Figs. 3, 4 and 5 by the dotted line 89 interconnecting the pivoted pointsof armature sections 15 and 16, which sections have been shown separated in these figures for convenience of illustration.

Engagement of the relay armature with either contact II or 12 will cause motor 30 to be energized through one field winding 66 or 61 for selective operation in reverse directions. Use of relay 7 '19 with the control circuit oi the invention permits any type or size of motor to be used for motor 30, depending upon the particular source of power economically available and the particular application for which the motor is intended.

The terminals of signal receiver rotor winding 24 are connected through leads 84 to the primary winding I8 of a grid transformer 80, thus impress ing the control signal thereon. Transformer 06 is provided with a pair of secondary windingsti and 82. A corresponding pair of terminals of windings 8i and 82 are connected, through limiting resistors 83 and 84, to control grids 85 and 88, respectively, of a pair of electronic amplifier tube paths 81 and 88. Tube paths WI and 88 are respectively provided with cathodes 80 and 9! interconnected to ground at 82, and with anodes 93 and 94. Anodes 93 and 94 are each connected to one terminal of a relay operating coil 73 or T4. The opposite terminals of coils i3, I4 are connected to the end terminals of the secondary winding 95 of a transformer 96 having a primary winding 9?. Primary winding 91] of the transformer is connected to a source oi alternating current which, for control purpose, is the same reference source to which rotor winding 28 is connected, and may be that indicated by the leads it of Fig. 1. It will be noted that the respective connections are such that the reference voltage is impressed in phase-opposition on anodes 93, 95, and the reference signal voltage is impressed in in-phase relation on grids t and fit.

The use of differential relay is is an important feature in the circuit of the invention as it contributes greatly to the accuracy, sensitivity and I.

stability of control. The single pivoted armature 88, common to both relay coils it and is, prevents accidental simultaneous energizing of motor 30 for reverse directions of rotation at the same time, as might occur, were two separate relay armatures used.

Under null conditions, the efiective bias of grids l transformer 80 to effectively operate their arms.-

. interconnected and grounded at I00. The other terminals of secondary windings 8| and 82 are connected, through condensers Ifll' and I08 to adjustable contacts I02 and I04 of potentiometer 98, respectively. Fixed resistors I05 and W0 are respectively connected in parallel with condensers WI and I08. One junction point of condenser [0| andresistor I05 is connected to anode 93 through resistor I0I. Similarly, a. junction point of condenser I03 and resistor I08 is connected to anode 94 through resistor I08.

- The operation of the control circuit shown in Fig; 3 is as follows. Contacts I02 and! are so adjusted as to bias grids 85 and 88 to condition tubes 8! and 88 to pass small and equal currents through coils i3 and I4, retaining armature 88 in its neutral or balanced position when rotors 23, 24 are in null relation. Upon a displacement of rotor winding 28 through movement of selector knob 2I, an alternating current control" or signal voltage is induced in rotor winding 24 and'impressed through leads 34 upon primary 18 of transformer 00. Through secondary windings I 8 i, 02 of the transformer, a proportionally higher 85 and B6 is such that tubes ti and 88 are conditioned to pass relatively small and equal currents through coils I3 and I4. In a typical practical example, such current might be of the order oi siX milliampere's. As the some current passes through both relay coils, there is no net effect on armature 89, and the latter remains in its neutral or balanced position. When a control signal is impressed on transformer 8% in response to rela= tive displacement of rotors 23 and 2d, the current flowing through one tube is increased and that through the other tube is decreased. For exam ple, such increase and decrease in current might be of the order of two milliamperes. The effective current through the selectively operated one of the relay coils would then be eight milliamperes whereas that through the otherrelay coil will be reduced to four milliamperes. The net relay or differential current operating the relay armature will therefore be four milliamperes.

The described effect greatly increases the sensi= tivity of response of differential relay it as com-=- pared to two separate relays. Under the same conditions, the current flowing through two separate relays must be reduced in value in order to prevent accidental operating of the separate relay armatures. If the current through one of such separate relays is increased due tothe imposition of a signal voltage on transformer 80, the decrease in current through the other relay will not assist in operation of the selected relay armature. Accordingly, a pair of separate relays require a greater signal voltage to be impressed on grid voltage is impressed in in-phase relation, on grids 85 and 88 of electronic tubes 81 and 88, through limiting resistors 83 and 84. Depending upon the direction of displacement of winding 23 from its previous null position, one tube 81 or 88 will become more conductive and the other less conductive. Transformer secondary winding 95 displaces the potential of anodes 83, 84 by 180 electrical degrees. The sense or phase of the resultant control signal will accordingly be in phase with the anode voltage of one or the other of tubes 81, 80 and render them selectively conductive. Of course, the grids may be energized in phase-opposition, and the anodes in in-phase relation, if desired.

In either event, the current through relay coils I3 and I4 willbe unbalanced to bias armature 89 into engagement with contact II or I2, dependent upon the relative phase of the control or signal voltage or sense of rotor 28 displacement. This operation effects energlzation of clutch unit 35 and motor through one of the latters field windings 65 or 61 in such a direction as to cause the motor to rotate in a direction to operate member 20 and bring receiver rotor winding 24 into angular coincidence with transmitter rotor winding 23. When the rotor windings are again in null relation, which occurs when movable member 20 substantially coincides in relative position with selector knob 21, the input signal voltage to grid primary winding I8 will be reduced to its null value, which conditions tubes 81 or 88 to be equally conductive, thus balancing the operating current of relay coils I3 and I4. Armature 89 is swung to its neutral or balanced position and the motor circuit is broken at contact ll or I2. Clutch-brake unit operates to substantially instantaneously stop actuator 45 andmovablemember 20, in a manner described in more detail hereinafter.

Despite such substantially instantaneous action of clutch-brake unit 35 in disconnecting motor 30 from actuator 45, there may be a tendency for motor 30 to move rotor winding 24 beyond its null position with respect to rotor winding I3. This will induce a reversely directed signal voltage into primary winding 18, causing tubes 81 and 88 to be conditioned to operate differential relay 18 to operate motor 30 in the reverse direction before a steady state is reached. A suitable anticipation or anti-hunt means is provided to prevent such tendency to hunt in the system shown in Fig. 3.

In the system illustrated in Fig. 3, the counter, or anti-hunt signal is derived in the following manner. Assuming that tube 81 is the one conditioned to be more conductive, an increased current will flow in both its plate and grid circuits. Through its connection to secondary winding 8i, condenser resistor combination IIII,

I is connected in the circuit of control grid 88.

Accordingly, a potential is impressed across condenser IOI causing a counter signal to be stored therein during the time knob 21 is being displaced with respect to movable member 20. The final voltage across condenser "II will be substantially equal to the peak voltage drop across resistance I05. As motor 30 starts to rotate member back into coincident relation with selector knob 21, and thus to rotate rotor winding 24 into null relation with rotor winding 23, the counter signal potential stored in condenser IIII is impressed upon grid 85. During such movement of member 20 into coincident relation with selector III, the charge on condenser IIiI gradually leaks oil. through resistor I'IIB.

However, this leaking action is at such rate that the counter signal potential from condenser IOI decreases at a rate less than the rate of decrease of the signalvoltage impressed on grid 85 from secondary winding 8I due to such movement. The counter signal potential is likewise in a direction to oppose the signal voltage impressed on grid 85 from winding 8i, and to oppose the activating potential impressed on anode 93 from transformer secondary winding 95.v

The effect of these two actions is to reduce the conductivity of tube 81 to normal or less than normal before rotor winding 2! has attained i'ull coincidence with rotor winding 28. That is, the effective activating voltage for tube 81, and the efiective signal voltage impressed on its grid 85, are decreased below the values they would normally be. Relay 19 accordingly operates its armature 89 to break the motor circuit at contact 1i. Movement of rotor winding 24 then stops, with winding 24 in a non-null relation with winding 23. However, the charge on condenser Ilii continues to leak oil throu h resistance I05. Accordingly, after an interval of time, the values of the activating potential applied to anode 93 and of the signal voltage applied to grid 85 become sumcient to again render tube 81 more conductive than tube 88. Thus, relay 19 again operates armature 89 to engage contact H and motor again moves rotor 24 toward a null relation with rotor 23. The result of the two actions described above is to effect a chattering-in or "stepping-in of motor 30, and hence of rotor 24, into the final or null position.

Resistors I 01 and I08, together with resistors I05 and I88, and potentiometer 98 form shunt 10 stored in condenser I OI. As tube 88 was made less conductive than normal, nocounter signal potential was stored in its associated condenser I 83. However, the signal voltage impressed on grid 88 of tube 88 from transformer 80 is the same as that impressed on grid 85 of tube 81. Accordingly, tube 88 remains at its full sensitivity with respect to the signal voltage impressed thereon. Should, despite the above arrangement, the rotor 24 overshoot its final position with respect to rotor 28, tube 88 would immediately become more conductive than normal to energize relay 19 in a direction to engage armature 88 with contact 12 and thus energize motor 38 for rotation in the reverse direction to angularly align member 20 and selector ID.

The effective result of the actions described above is to shift" the null zone in the direction of the original displacement of knob 21 with respect to movable member 20. Accordingly,

.eflective inhibition of hunting is accomplished circuits around the loads represented by relay coils 13-ancl 14. As the flow of current through 13 or 14 increases, the bias on the associated grid or 86 is reduced.

In the example cited above, tube 81 was the one made more conductive than normal. and hence a substantial counter signal potential was r the invention may assume in practice.

as rotor 24 is moved in the opposite direction toward null relation with rotor 23. At the same time, the sensitivity of the circuit to movement of selector knob 21 in the opposite direction is not destroyed, as the other tube 31 or 88 remains fully sensitive to effect energization of motor 38 in the reverse direction.

Fig. 4 illustrates another embodiment which To simplify the drawing, signal transmitter I5 and signal receiver 55 and their connections, and motor 38, clutch-brake unit 35 and their connections, outside the broken lines of Fig.8, have been omitted. It is to be understood that such connections are identical with those in Fig. 3. Likewise, the parts of Fig. 4 corresponding to Fig. 3 have been given identical reference numerals. Resistors I01, I08, and the arrangements shown in Fig. 4, do not form part of shunt circuits as in Fig. 3. Here, these resistors operate only to give feedback characteristics due directly to the anode connection, and to limit the flow from plate to ground when the relays are closed.

In the embodiment shown in Fig. 4, the signal irom rotor winding 24 is again impressed through leads 34 on primary winding 18. The secondary windings 8| and 82 are connected to grids 85 and 86 in the same manner as in Fig. 3. Similarly, the opposite pair of terminals of windings 8| and 82 are connected through resistors Q01 and M18 respectively to anodes 93 and 94. However, the resistor-condenser combinations iili, I95 and I03, I06 of Fig. 3, are omitted.' Transformer 96 is provided with a primary winding 91 and a split secondary winding 95, 95. The ground point 92 for cathodes and SI is connected to the common junction iIil of windings 95 and 95.

Front contact 1! is connected through a conductor III and a condenser H2 to the grid and anode circuits of tube 81. The connection to the anode circuit is made through resistor E01, and that to the grid circuit through secondary winding 8i and limiting resistor 83. In a similar manner, front contact 12 is connected through conductor H3 and condenser H4 to the anode and grid circuits of tube 88. v

The anti-hunting arrangement shown in Fig. 3, is efiective only upon relatively large displacements of rotors 23 and 24 due to the time necessary for an effective counter potential to be built up in the resistance-condenser anticipation arrangement. Accordingly, the anticipation arrangement of Fig. 3 is not effective for relatively small displacements of rotors 23 and 24. The

enn similar to that illustrated in Fig 3, with as anti-hunting or anticipation arrangement eflective on small relative displacements of the rotors 23, 24 being superposed thereon. Accordingly.

elements identical with those in Fig. 3 have been given the same reference numbers.

The operation 01 the control circuit illustrated in Fig. 5 on relatively large displacements oi rotors are connected to windings 85 and 95 in phaseopposition. Accordingly, one tube 8'5 or 88 will become more conductive and the other less con ductive depending upon the direction oi relative displacement of position selector knob 27] with respect to movable member it. let us assume that, under a given set cl conditions, the dis= placement is in such a direction to make 87 more conductive. Under such conditions, the current through relay coil ill will be increased and that through coil 16 decreased, thus engaging armature section it with contact ii to energize motor to and clutch-brake unit 35 in direction" to rotate shaft to to restore movable member to a coincident position with respect to selector knob 27.

Immediately upon engagement oi armature d9 with contact ll the alternating current potentials applied to the anode and grid circuits of tube iii are grounded at the negative terminal oi source ill through condenser lid and conductor ill. Condenser I I2 prevents the flow of direct current through conductor ill. Such grounding eilects a sharp reduction in the eflective values of the A. C. activating potential and'signal voltage applied to tube 8?. Accordingly, with a relatively small displacement resulting in a relatively small signal voltage bein impressed on grids 85 and 8%, the conductivity 0! tube 8'17 is immediately decreased to normal, operating relay 19 to break the energizing circuit oi motor 88 and disconnect the same from movable member 28 through clutchbrake unit 35. However, such anticipation effect is only momentary. Should the displacement oi knob 2l with respect to member 29 be relatively large, the reduction in the A. C. signal voltage and activating potential will not be sumcient to immediately reduce the conductivity of tube 8i to normal.

However, when movablemember 20 has almost reached the position of coincidence with selector knob 21, the signal voltage will be reduced to a value where it is lnsuficient to condition tubes 87 and 88 and relay l9 to energize motor co. De energization of motor 80 immediately removes the negative potental connection from the grid and anode circuits of tube 87. Accordingly, if the rotors 28 and 24 are not in null relation, a signal voltage will still be impressed on grid 85 which will again condition tubes 81 and 88 to operate relay 19 to engage armature 88 with contact H. The resultis to effect a chattering-in or steppingin of motor to the final position in a manner similar to that described inFig. 3.

It will be notedthat the described desensitizing efiect takes place only with respect to one tube 8? or 88. The other tube remains fully sensitive so that, in the event selector lmob 21 is displaced in the opposite direction, the control system will respond immediately to such opposite displacement. This greatly increases the sensitivity or the control circuit. 1

Fig. 5 illustrates another embodiment of the control circuit of the invention including antihunting or anticipation means .efiective on both small and large relativedisplacements of rotor 23 and 24. The circuit illustrated in Fig. 5 is gen- 23 and 24 with respect to each other is identical to that described in connection with Fig. 3. 'lhat is, a counter signal potential is built up on either condenser till or we depending upon which of the tubes bl, 88 is made more conductive than the other. This counter signal potential, during oper ation of the motor. to restore coincidence between member at and selector illopposes the signal volt age impressed on grids 85 and to ciiect a rehab Bil once of the conductivities of tubes 8?] and 88 be lore the position selector and the movable mem her have obtained substantially full coincidence. This accordingly effects a shitting oi the null zone in the same manner as described in connection with Fig. 3 while retaining the circuit at its lull sensitivity for any further displacement oi the selector in the opposite direction from that oi the original displacement.

To provide anticipation and anti-hunting on relatively small displacements of rotors 23 and 24, grid 85 is connected to vfront contact ll of relay l5 through a conductor Hi5 and a condenser H8. Similarly, grid 86 is connected to front contact 12 of relay '55 through a-conductor ill and a con denser H8. Accordingly, immediately upon oper ation of differential relayi9, either grid 85 or 85 is connected through armature 89 and contact ll or 12 to the negative terminal of source ill. The A. C. signal potential is thus grounded, the voltage reduction being limited by grid resistors 88, 84. This immediately reduces the bias of grid 85 or 86 to a value insufllcient to make its associated tube 81 or 88 more conductive than the other tube. Accordingly, the tubes immediately become equally conductive, disengaging armature 89 from contact II or l2 to deenergize motor 88. Upon such disengagement or" relay armature 89, the ground is removed from the A. C. signal potential applied to grid 85 or 88 and they signal voltage is then sufilcient to condition tubes 8'? and 88 to actuate differential relay l9. The result of these actions is to efiect a chattering-in or stepping-in oi the rotors 23,01 24 into their substantially null position.

Upon relatively large displacement of rotors 23 and 24 with respect to each other, the A. C. signal voltage impressed on grids 85 and 88 from transformer is suificiently large in value that the partial grounding thereof through closure of relay armatures 89 in either direction is insufficient to reduce the effective signal voltage below a value sufilcient to condition the tubes to actuate relay 18. However, on such relatively large displacement, the anti-hunting arrangement including the two condenser-resistance combinations takes control and likewise effects a chattering-in orstepping-in of the motor into the final position in the manner previously described. It will be noted that Fig. 5 includes two anticipation or anti-hunting arrangements, one eflective during relatively large displacements of the position selector and movable member and one effective during relatively small displacements thereof. Accordingly, Fig. 5 is a circuit of universal applicability due to its effective operation on elther'small or large relative displacements of rotors 23 and 24.

It hould be understood, however, that both the .assignee as the present case.

anticipation eflect on relatively large displace- 'ments and the anticipation eilfect on relatively small displacements are operable not alternaaverage-displacement of the signal transmitter and receiver rotors from their null position, the

resistance-condenser combination will effect anticipation during restoring movement of the receiver rotor from its maximum displacement until the rotors are almost in the null position. At such time, the eii'ect of the resistor-condenser combination on the system will be relatively less strong than the effect of the relay fkick-back anticipation eflect thereon. Accordingly, during the final movement of the receiver. rotor into its null relation with the transmitter rotor, the relay "kick-back" anticipation effect will control. Thus, both anticipation effects are operative during an average displacement of the rotors from their null relation.

An important feature of the present invention is the electromagnetic clutch and brake unit 35 provided for connecting motor 30 to jack screw 45. As explained above, the clutch and brake unit is in electric circuit relation with motor 30 so that it is energized when motor 30 is energized to instantly couple the motor to the Jack screw actuator. When motor 30 is deenergized, clutch unit 35 is immediately deenergized and instantly brakes the actuator and associated elements. This action is very effective in preventing overshooting and hunting of the motor drive and of the control system. The efiect of motor momentum is minimized. The electromagnetic clutch and brake unit 35 may be of the type described and claimed in Patent No. 2,267,114 entitled Electromagnetic clutch issued December 23, 1941 to William P. Lear, or Patent No. 2,401,003 entitled Electromagnetic clutch issued May 28, 1946 to William P. Lear, both assigned to the same For purpose of illustration, the electromagnetic clutch and brake unit described in said latter patent is illustrated inFig. 6.

Referring to Fig. 6, the electromagnetic clutch and brake unit 35 includes a driving member I35 of magnetic material having a hub portion I38 keyed to the shaft I31 of armature 55 of motor 30. Armature shaft I31 is provided with a. reduced extension i38. Mounted on extension I38 is driven clutch member I39 likewise of magnetic material and having a hub portion I40 concentric with extension I38 and supported thereon through ball bearings I4I. Hub portion I40 is provided with a reduced extension I42 which is mounted on ball bearings M3 in a member I45 disposed in a.

housing I46. Drive pinion 41 is mounted in the outer end of extension I42- A housing I44 of magnetic material surrounds hub portion 136 of driven member I35, the housing being completed by an extension I41 of housing I45.

Mounted in the compartment thus formed is a magnetizing winding I48 which is preferably connected in electric circuit relation with motor 30 either in series or parallel relation. A brake surface I49 of suitable material, such as cork, is mounted in housing I45 adjacent driven clutch member I38. A spring I50 surrounding armature shaft extension I38 abuts driving member 535 and ball bearing assembly I4! to normally urge driven member I39 into engagement with brake surface I43. As described in said Patent No. 2,267,114, driving member I35 may be provided with one or more inserts II of non-magnetic material to increase the number of mag- J netic flux interlinkages between the driving and driven members oi the clutch. Upon energization of winding I48, driven member I38 is magnetically attracted into frictional and magnetic coaction with driving member I35 to couple armature shaft I31 to pinion 41. The

magnetic attraction between the driving and driven members overcomes the force of spring H50. Upon deenergization of winding I48, which preferably occurs simultaneously with deenergization of motor 80, spring I snaps driven disk I39 into instantaneous engagement with brakin surface I49. This instantly disconnects motor 30 from pinion 41 and effects immediate stopping of the driven system connected to pinion 41. The armature 65 of motor 30 may rotate at a decreasing rate due to the stored kinetic energy without moving pinion 41. Accordingly, any tendency for the driven system connected to pinion 41 to hunt on either side of the null position, is effectively inhibited due to the instantaneous braking action of clutch and brake unit 35 when motor 30 is deenergized in response to the control signal reaching zero when signal transmitter I5 and signal receiver are in nullrelation. The clutch and brake unit is particularly efiective in small or inching" movements of the system.

While specific embodiments of the invention have been described for the purpose of illustrating the principles thereof, it will be obvious to those skilled in the art that the invention may be otherwise embodied. without departing from such principles.

What is claimed is: 1. A position control system for a movable member comprising, in combination, an electric motor operable to position the member; switch means selectively operable to connect said motor to a source of power for rotation in either direction; a pair of electronic tube paths selectively controlling the operation of said switch means; means, including circuit connections, for impressing a control signal voltage on the control grids of said tube paths to selectively condition one of said tube paths to selectively operate said .7

switch means; and means, in individual. circuit connection with the anode of each of said tube paths, eiiective to render the selectively conditioned tube path less sensitive than the other tube path-to effect deenergization of said motor before the movable member attains a position corresponding to the control signal to inhibit hunting of the movable member.

2. A position control system for a movable member comprising, in combination, an electric motor operable to position the member; switch means selectively operable to connect said motor to a source of power for rotation in either direction; a pair of electronic tube paths selectively controlling the operation of said switch means: means, including circuit connections, for impressing a control signal voltage on the control grids of said tube paths to selectively condition one of said tube paths to selectively operate said switch means; and means, in individual circuit connection with the anode of each of said tube paths, for storing a counter signal potential cor responding to the magnitude of the signal voltage and effective to render the selectively conditioned tube path less sensitive than the other tube path to effect deenergization of said motor before the movable member attains a position corresponding to the control signal to inhibit hunting of the movable member.

3. A position control system for a movable member 7 comprising, in combination, an electric motor operable to position the member; switch means selectively operable to connect said motor I means; and means, in individual circuit connec tion with the anode of each oi said tube paths,

operable in response to operation oi said switch means to decrease the operating potential or the selectively conditioned tube path to render the selectively conditioned tube path less sensitive than the other tube path to chest deenergizationor? said motor before the movable member attains a position corresponding to the control signal to inhibit hunting oi the movable member.

6. A position control system for a movable xncin= her comprising, in combination, an electric motor operable to position the member; switch means selectively operable to connect said motor to a source of power for rotation in either direction;

tential upon its associated tube path in opposition to the signal voltage impressed upon the control grid thereof to condition said tube paths to operate said mechanism to deenergize said motor and disconnect it from said device before such condition has been restored to such reference value to inhibit hunting of the control system; the effective signal voltage on the contrcl grid of the other tube path reaching a value ,insumcient to condition said tubes to effect energisation of said motor only when such condition has substantially reattained such reference value.

A motor control circuit comprising an electric motor; a device operable to vary the value of a given condition with respect to a reference value; mechanism, including a differential rea pair oi electronic tube paths selectively con= trolling the operation of said switch means;

means, including circuit connections, for impress= ing a'control signal voltage on the control grids of said tube paths to selectively condition one a: said tube paths to selectively operate said switch means; means, in individual circuit condeenergization of said motor before the movable member attains a position corresponding to the control signal to inhibit hunting of the movable member; and means, in individual circuit connection with each oi said tube paths, operable in response to operation of said switch means to decrease the operating potential oi the selective ly conditioned tube path to render the selectively conditioned tube path less sensitive than the other tube path to effect deenerglzation of said motcr before the movable member attains a position corresponding to the control signal to inhibit hunting of the movable member.

5. A motor control circuit comprising an electric motor; a device operable to vary the value of a given condition with respect to a reference value; mechanism, including a diflerential relay having a pair of operating coils and a pivoted armature, operable to connect said motor to a source of power and to said device; a pair of electronic tube paths each connected in circuit relation with one of said relay operating coils and selectively operable, when conditioned, to operate said mechanism and said rela means responsive to a change in such condition from such reference value to impress on the grid circuit of said electronic tube paths a signal voltage proportional to such change to selectively condition said electronic tube paths to operate said mechanism to energize said motor and connect it to said device to operate the latter in a direction to restore such condition to such reference value; and separate means each connected in individual circuit relation with the anode and-control grid circuit of one of said tube paths for storing a counter signal potential during activation of its associated tube proportional to such condition change and impressing such counter signal polay having a pair oi operating coils and a pivoted armature, operable to connect said motor to a source of power and to said device; a pair of electronic tube paths each connected in circuit relation with one oi said relay operating coils and selectively operable, when conditioned, to operate said mechanism and said relay; means responsive to a change in such condition from such refe'rence value to impress on the grid circuit of said electronic tube paths a signal voltage proportional to such change to selectively condition said electronic tube paths to operate said mechanism to energize said motor and connect it to said device to operate the latter in a direction to restore such condition to such reference value; and circuit means individual to each tube path and operative immediately upon energizetlon or said relay to reduce the operating potential applied from such reference source to the associated tube path to condition said tube paths to operate said mechanism to deenergize said motor and disconnect it from said device before such condition has been restored to such reference value to inhibit hunting of the control system; the operating potential applied to the other tube path. remaining unchanged during such movement.

7. A motor control circuit comprising an electric motor; a device operable to vary the value of a given condition with respect to a reference value; mechanism, including a differential relay having a pair of operating coils and a pivoted armature, operable to connect said motor to a source of power and to said device; a pair of electronic tube paths each connected in circuit relation with one of said relay operating coils and selectively operable, when conditioned, to operate said mechanism and said relay; means responsive to a change in such condition from such reference value to impress on the grid circuit of said electronic tube paths a signal voltage proportional to such change to selectively condition said electronic tube paths to operate said mechanism to energize said motor and connect it to said device to operate the latter in a direction to restore such condition to such reference value; separate means each connected in individual circuit relation with the anode and control grid circuit of one of said tube paths for storing a counter signal potential during activation of its associated tube proportional to such condition change an impressing such counter signal potential upon its associated tube path in opposition to the signal voltage impressed upon the control grid thereof to condition said tube paths to operate said mechanism to deenerglze said motor and disconnect it from said device before such condition has been restored to such reference value to inhibit hunting of the control system; the

effective signal voltage on the control grid of the other tube path reaching a value insufllcient to condition said tube paths to effect energization of said motor only when such condition has substantially reattained such reference value; and other hunting inhibiting means comprising circuit means individual to each tube path and operative upon energization of said relay to reduce the operating potential applied from such reference source to the associated tube path to con dition said tube paths to operate said mechanism to deenergize said motor and disconnect it from said device before such condition has been restored to such reference value to' inhibit hunting of the control system; the operating potential applied to the other tubepath remaining unchanged during such movement.

8. A remote positioning control system for a movable member comprising, in combination, a position selector; a signal transmitter operatively associated with said selector; an actuator effective to position the movable member; an electric motor; mechanism, including relay means, operable to connect said motor to a source of power and mechanically to said actuator; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of electronic tubes each connected in circuit relation with one of said relay means and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively condition said tubes to actuate said mechanism and operate said relay means to energize said motor and connect it to said actuator for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincldcnt relation of the movable member and said selector corresponding to a null zone in which the resultant eflective value of the signal voltage impressed on said tubes is insufiicient to condition said tubes to operate said mechanism; means connected in individual circuit relation with the anode of each of said tubes for storing a counter signal potential during movement of said selector and the movable member out of coincidence and corresponding to the resultant relative displacement of said transmitter and receiver; and circuit means for impressing such counter signal potential on the associated one of said tubes in a direction to oppose the signal voltage thereon during movement of the member and said selector into coincidence, such counter signal potential exceeding such signal voltage when the member and said selector approach coincidence to shift such null zone in a direction to condition said tubes to operate said mechanism to deenergize said motor and disconnect it from said actuator before the movable member and said selector attain coincidence, whereby to inhibit relative hunting thereof; the effective signal voltage on the other tube reaching a value suificient to condition said tubes to effect energization of said motor only when the movable member and said selector have attained substantially full coincidence.

9. A remote positioning control system for a movable member comprising, in combination, a, position selector; 3. signal transmitter operatlvely associated with said selector; an actuator efiective to position the movable member; an electric motor; mechanism, including relay means, operable to connect said motor to a source 0! power and mechanically to said actuator; a sig-, nal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of electronic tubes each connected in circuit relation with one of said relay means and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on said tubes in. response to signals derived by said receiver from said transmitter when saidselector and the movable member are out of coincidence to selectively condition said tubes to actuate said mechanism and operate said relay means to energize said motor and connect it to said actuator for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincident relation of the movable member and said selector corresponding to a nu l zone in which the resultant eflective value of the signal voltage impressed on said tubes is insuflicient to condition said tubes to operate said mechanism; means connected in individual circuit relation with the anode of each of said tubes for storing a counter signal potential during movement of said selector and the movable member out of coincidence and corresponding to the resultant relative displacement of said transmitter and receiver; and circuit means for impressing such counter signal potential on the associated one of said tubes in a direction to oppose the signal voltage thereon during movement of the member and said selector into coincidence, and including means for dissipating such stored counter signal potential, as the member and said selector are moved toward coincidence, at a rate less than the rate of decrease of such signal voltage due to such movement; such counter signal potential exceeding such signal voltage when the member and said selector approach coincidence to shift such null zone in a direction to condition said tubes to operate said mechanism to deenergize said motor and disconnect it from said actuator before the movable member and said selector attain coincidence, whereby to inhibit relative hunting thereof; the effective signal voltage onv the other tube reaching of a value sufficient to condition said tubes to effect energization of said motor only when the movable member and said selector have attained substantially full coincidence,

10, A remote positioning control system for a movable member comprising, in combination, a position selector; a signal transmitter-operatively associated with said selector; an actuator effective to position the movable member; an electric motor; mechanism, including relay means, operable to connect said motor to a source of power and mechanically to said actuator; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of electronic tubes each connected in circuit relation with one of said relay means and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively condition said tubes to actuate said associated with said selector;

mechanism and operate said relay means to energize said motor and connect it to said actuator for rotation in a direction to restorecoincidence between the movable member and said selector; a substantially coincident relation of the movable member and said selector corresponding to a null zone in which the resultant effective value of the signal voltage impressed on said tubes is insuflicient to condition said tubes to operate said mechanism; and circuit means individual to the anode of each tube and operative upon energization of said relay means to reduce the operating potential applied from such reference source to the associated tube to shift the null zone in a direction to condition said tubes to operate said mechanism to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof on either side of the null zone; the operating potential applied to the other tube remaining unchanged during such movement.

11. A remote positioning control system for a movable member comprising, in combination, a position selector; a signal transmitter operatively tive to position the movable member; an electric motor; mechanism, including relay means, operable to connect said motor to a source of power and mechanically to said actuator; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of electronic tubes each connected in circuit relation with one of said relay means and a reference source of alternating current; means including" circuit connections for selectively impressing a signal voltage from such reference source on said tubes in response to signals derived by said receiver from'said transmitter when said selector and the movable member are out of coincidence to selectively condition said tubes to actuate said mechanism and operate said relay means to en ergize said motor and connect it to said actuator for rotation in a direction to restore coincidence.

between the movable member and said selector;

, a substantially coincident relation of the movable member and said selector corresponding to a null zone in which the resultant effective value of the signal voltage impressed on said tubes is insuflicient to condition said tubes to operate said mechanism; a first anti-hunting null shifting circuit arrangement comprising means connected in individual circuit relation with each of said tubes for storing a counter signal potential during movement of said selector and the movable member out of coincidence and corresponding to the resultant relative displacement of said transmitter and receiver, circuit means for impressing such counter signal potential on the associated tube in a direction 'to oppose such signal voltage during movement of the member and said selector into coincidence, and including means for dissipating such stored counter signal potential, as the member and said selector are moved toward coincidence, at a rate less than the rate of decrease of such signal voltage due to such movement, such counter signal potential exceeding such signal voltage when the member and said selector approach coincidence to shift such null zone in a direction to condition said tubes to operate said mechanism to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof, the effective signal voltage on the other tube reaching an actuator effec- 20 a value insuflicient to condition said tubes to effect energization of said motor only when the movable member and said selector have attained substantially full coincidence; and a second antihunting null shifting circuit arrangement comprising circuit means individual to each tube and operative upon energization of said relay means to reduce the operating potential applied from each of said tubes for storing a counter signal such reference source to the associated tube to shift the null zone in a direction to condition said tubes to operate said mechanism to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof on either side of the null zone, the operating potential applied to the other tube remaining unchanged during such movement; such first circuit arrangement being effective upon relatively large relative displacements of 1 said transmitter and receiver and such second circuit arrangement being effective upon relatively small relative displacements of said transmitter and receiver.

12. A remote positioning control system for a movable member comprising, in combination, a position selector; 9. signal transmitter operatively associated with said selector; an actuator effective to position the movable member; an electric motor; relay means, operable to connect said motor to a source of power; a clutch operable, simultaneously with energization of said motor, to connect the same to said actuator and, simultaneously with deenrgization of said motor, to disconnect the same from said actuator; brake means effective upon deenergization of said motor to arrest motion of said actuator and of the movable member connected thereto; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of electronic tubes each connected in circuit relation with one of said relay means and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on said tubes in response to signal derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively condition said tubes to actuate said mechanism and selectively operate said relay means to energize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincident relation of the movable member and-said selector representing a null zone in which the effective value-of the signal voltage impressed on said tubes is insuflicient to condition said tubes to operate said mechanism; means connected in individual circuit relation with the anode of potential during movement of said selector and the movable member out of coincidence and corresponding to t e resultant relative displacement of said transmitter and receiver; and circuit means.

for impressing such counter signal potential on the associated one oi said tubes in a direction to oppose the signal voltage thereon during movement of the member and said selector into coincidence, such counter signal potential exceedin such signal voltage when the member and said selector approach coincidence to shiftsuch null zone in a direction to condition said tubes to operate said relay means to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence,

. associated with said selector; an actuator eifective to position the movable member; an electric motor; differential relay means including apair of operating coils and a pivoted armature operable to connect said motor to a source of power; an

electromagnetic clutch operable, simultaneously -with energizatlon of said motor, to connect the same to said actuator and, simultaneously with deenergization of said motor, to disconnect the same from said actuator, and brake means effective upon deenergization of said motor to arrest motion of said actuator and thus oi. the movable member connected thereto; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair. of electronic tubes each connected in circuit relation with one oi said relay operating coils and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on said tubes in response to signals derived by said receiver from said transmittr when said selector and the movable member are out of coincidence to selectively increase the conductivity of one of said tubes and decrease the conductivity of the other to unbalance the current through said relay operating coils to operate said armature to enercize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincident relation of the movable member and said selector representing a null zone in which the effective value of the signal voltage impressed on said tubes is insufllcient to condition said tubes to operate the relay armature; means connected in individual circuit relation with the anode of each of said tubes for storing a counter signal potential during movemnt of said selector and the movable member out of coincidence and a the signal voltage on the associated tube when the member and said selector approach coincidence to shift such null zone in a direction to equalize the conductivity of said tubes and. the operating currents of said relay coils to operate said relay armature to a neutral position to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof, the effective signal voltage on the other tube reaching a value insufficient to condition said tubes -to effect energization of said motor onlyv when the movable member and said selector have attained substantially full coincidence.

14. A remote positioning control system for a movable member comprising, in combination, a position selector; a signal transmitter operatively associated with said selector; an actuator effective to position the movable member; an electric motor; differential relay means including a pair of operating coils and a pivoted armature operable to connect said motor to a source of power; an electromagnetic clutch and brake unit including a clutch operable, simultaneously with energization of said motor, to connect the same to said actuator and, simultaneously with deenergization of said motor, to disconnect the same from said actuator and brake means eflective upon deenergization of said motor to'arrest motion of said actuator and thus of the movable member connected thereto; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of electronic tubes each connected in circuit relation with one of said relay operating coils and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on said tubes in response to signals derived by said receiver from said reference source on said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively increase the conductivity of one of said tubes and decrease the conductivity of the other to unbalance the current through of the movable member and said selector representing a null zone in which the effective value of the signal voltage impressed on said tubes is insuflicient to condition said tubes to operate the relay armature; a first anti-hunting null shifting circuit arrangement comprising means connected in individual circuit relation with each of said tubes for storing a counter signal potential during movement of said selector and the movable member out of coincidence and corresponding to the resultant relative displacement of said transmitter and receiver, circuit means for impressing such counter signal potential on the associated tube in a direction to oppose such signal voltage during movement of the member and said selector into coincidence, and including means for dissipating such stored counter signal potential, as the member and said selector are moved toward coincidence, at a rate less than the rate of decrease of such signal voltage due to such movement, such counter signal potential exceeding such signal voltage when the member and said selector approach coincidence to shift such null zone in a direction to condition said tubes to operate said mechanism to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof, the eifective signal voltage on the other tube reaching a value insufficient to condition said tubes to effect energization of said motor. only when the movable member and said selector have attained substantially full coincidence; and a second anti-hunting null shifting circuit arrangement comprising circuit means individual to each tube and operative able,

23 "upon energization of said relay means to reduce the operating potential applied from such reference source to the assocated tube to shift the null zone in a direction to condition said tubes to operate said mechanism to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof on either side of the null zone, the operating potential applied to the other tube remaining unchanged during such movement; arrangement being effective upon relatively large relative displacements of said transmitter and receiver and such second circuit arrangement being effective upon relatively small relative displacements of said transmitter arid receiver.

15. A remote positioning controb system for a movable member comprising, in combination, a position selector; a signal transmitter'operatively associated with said selector; an actuator eifective to position the movable member: a direct current electric motor; differential relay means including a pair of operating coils and a pivoted armature operable to connect said motor to a source of direct current; an electromagnetic clutch and brake unit including a. clutch oper simultaneously with energization of said motor, to connect the same to said actuator and, simultaneously with deenergization of said motor, to disconnect the same from said actuator; brake means effective upon deenergization of said motor to arrest motion or said, actuator and thus of the movable member connected thereto; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said transmitter and receiver; a pair of electronic tubes each connected in circuit relation with one of said relay operating coils and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively increase the conductivity of one of said tubes and decrease the conductivity of the other to unbalance the current through said relay operating coils to operate said armature to energize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincident relation of the movable member and said selector representing a null zone in which the effective value of the signal voltage impressed on said tubes is 'insuflicient to condition said tubes to operate the relay armature; means connected in individual circuit relation with the anode of each oigaid tubes for storing a counter signal potential during movement of said selector and the movable member out of coincidence and corresponding to the resultant relative displacement of said transmitter and receiver and in-- cluding means for dissipating such stored counter signal potential, as the member and said selector are moved toward coincidence, at a rate less than the rate of decrease of such signal voltage due to such movement; and circuit means for impressing such counter sign-a1 potential on the asso-- ciated one of said tubes in a direction to oppose the signal voltage thereon during movement of the member and said selector into coincidence, such counter signal potential exceeding the signal voltage on the associated tube when the member and said selector approach coincidence to shift such first circuit such null zone in a direction to equalize the conductivity of said tubes and the operating currents of said relay coils to operate said relay armature to a neutral position to deenergize said motor and disconnect it from said actuator before the memhen-and said selector attain coincidence, whereby to inhibit relative huntingthereof; the eflectiveslgn-al voltage on the other tube reaching a value insuili'cient to condition said tubes to eflect energization of said motor only when the movable member and said selector have attained substantially full coincidence.

16. A remote positioning control system for a movable member comprising, in combination, a position selector; a signal transmitter operatively associated with said selector; anactuator efl'ective to position the movable member; a direct current electric motor; diiierential relay means including a pair of operating coils and a pivoted armatureoperable to connect said motor .to a source of direct current; an electromagnetic clutch and brake unit including a clutch operable, simultaneously with energization of said motor, to connect the same to said actuator and, simultaneously with deenergizatlon of said mo- .tor, to disconnect thesame from said actuator; brake means effective upon deenergizatlon of said motor to arrest motion of said actuator and thus of the movable member connected thereto; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said transmitter and receiver; a pair of electronic" tubes each connectedin circuit relation with one of said relay operating coils and a reference source oi. alternating, current; means including circuit connections forpselectively impressing a signal voltage from such reference source on said tubes in response to signalsidee rived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively increase the conductivity oi one of said tubes and decrease the conductivity of the other to unbalance the current through said relay operating coils to operate said armature to energize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector;

-a substantially coincident relation of the mov- "to equalize the conductivity of said tubes and the operating currents of said relay coils to operate said relay armature to a neutral position to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof; the operating potential applied -to the other tube remaining unchanged during such movement.

17. A remote positioning control system for a movable member comprising, in combination, a position selector; a signal transmitter operatively associated with said selector; an actuator eflec- -tive to position the movable member; a direct current electric motor; a difierential relay including a pair of operating coils and a pivoted armature operable to connect said motor to a source 25 of direct current; a clutch operable upon energization of said motor to connect the latter to said actuator; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of' grid-controlled electronic tubes each connected in circuit relation with one of said relay operating coils and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on the control grids of said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively increase the conductivity of one of said tubes and decrease the conductivity of the other to unbalance the operating currents in said relay coils to selectively operate said relay armature to energize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincident relation of the movable member and said selector representing a null zone in which the effective value of the signal voltage impressed on said tubes is insufiicient to condition said tubes to effect energization of said motor; separate means connected in individual circuit relationwith the anode and grids of each of said tubes. each operative to store a counter signal potential upon increase in the conductivity of its associated tube during movement of said selector and the movable member out of coincidcncc and corresponding to the resultant relative displacement of said transmitter and receiver; and circuit means for impressing such counter signal potential on the anode and grid of the associated tube in a direction to oppose the signal voltage thereon during movement of the member and said selector into coincidence, such counter signal potential exceeding the signal voltage on the associated tube when the member and said selector approach coincidence to shift such null zone in a direction to equalize the conductivity of said tubes to effect operation effect ve to position the movable member; a direct current electric motor; a differential relay including a pair of operating coils and a pivoted armature operable to connect said motor to a source of direct current; a clutch operable upon energization of said motor to connect the latter to said actuator; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of grid-controlled electronic tubes each connected in circuit relation. with one of said relay operating coils and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on the control grids of said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively increase the conductivity of one of said tubes and decrease the conductivity of the other to unbalance the operating currents in said relay coils to selectively operate said relay armature to energize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincident relation of the movable member and'said selector representing a null zone in which the effective value of the signal voltage impressed on said tubes is insufficient to condition said tubes to effect energization of said motor; a pair of capacitances each connected in series circuit relation with an anode and grid of one of said tubes; a pair of impedances each connected in parallel circuit relation with one of said capacitances; the capacitance associated with the tube having increased conductivity, during movement of said selector and the movable member out of coincidence, storing a counter signal potential corresponding to the resultant relative displacement of said transmitter and receiver; such counter signal potential, during movement of the movable member and said selector toward coincidence, being impressed on the anode and control grid of the associated tube in a direction to oppose the signal voltage impressed on the control grid thereof; and said impedance, during such latter movement, dissipating such counter signalpotential at a rate less than the decrease in such signal voltage responsive to such movement, whereby such counter signal potential exceeds such signal volt; age when the member and said selector approach coincidence to shift such null Zone in a direction to decrease the conductivity of the associated tube to equalize the conductivity of said tubes to effect operation of said relay armature to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereb to inhibit relative hunting thereof; the effective signal voltage on the control grid of the other tube reaching a value insufficient to condition said tubes to effect energization of said motor only when the movable member and said selector have attained substantially full coincidence.

19. A remote positioning control system for a movable member comprising, in combination, a position selector; a signal transmitter operatively associated with said selector; an actuator effective to position the movable member; a direct current electric motor; a differential relay including a pair of operating coils and a pivoted armature operable'to connect said motor to a source of direct current; a clutch operable upon energization of said motor to connect the latter to said actuator; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of grid-controlled electronic tubes each connected in circuit relation with one of said relay operating coils and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on the con.- trol grids of said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively increase the conductivity of one of said tubes and decrease the conductivity of the other to unbalance the operating currents in said relay coils to selectively operate said relay armature to energize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coincident relation of the movable member and said selector representing a null zone in which the effective value of the signal voltage impressed on said tubes is insufficient to condition said tubes to effect energization of said motor; separate means connected in individual circuit relation with the anode of each of said tubes, each operative to store a counter signal potential upon increase in the conductivity of its associated tube during movement of said selector and the movable member out of coincidence and corresponding to the resultant relative displacement of said transmitter and receiver; and circuit means for impressing such counter signal potential on the anode and grid of the associated tube in a direction to oppose the signal voltage thereon during movement of the member and said selector into coincidence, such counter signal potential exceeding the signal, voltage on the associated tube when the member and said selector approach coincidence to shift such null zone in a direction to equalize the conductivity of said tubes to effect operation of said relay armature to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit relative hunting thereof; the effective signal voltage on the other tube reaching a value insuffi cient to condition said tubes to effect energization of said motor only when the movable member and said selector have attained substantially full coincidence.

20. A remote positioning control system for a removable member comprising, in combination, a position selector; a signal transmitter operatively associated with said selector; an actuator effective to position the movable member; a direct current electric motor; a differential relay including a pair of operating coils and a pivoted armature operable to connect said motor to a source of direct current; a clutch operable upon energization of said motor to connect the latter to said actuator; a signal receiver operable in accordance with movement of the movable member; electrical means connecting said receiver and said transmitter; a pair of grid-controlled electronic tubes each connected in circuit relation with one of said relay operating coils and a reference source of alternating current; means including circuit connections for selectively impressing a signal voltage from such reference source on the control grids of said tubes in response to signals derived by said receiver from said transmitter when said selector and the movable member are out of coincidence to selectively increase the conductivity of one of said tubes and decrease the conductivity of the other to unbalance the operating currents in said relay coils to selectively operate said relay armature to energize said motor and connect it to said actuator through said clutch for rotation in a direction to restore coincidence between the movable member and said selector; a substantially coinci- 28 selector representing a null zone in which th effective value of the signal voltage impressed on said tubes is insuiiicient to condition said tubes to effect energization of said motor; a first antihunting null shifting circuit arrangement comprising a pair of capacitances each connected in series circuit relation with an anode and grid of one of said tubes; a pair of impedances each connected in parallel circuit relation with one of said capacitances; the capacitance associated with the tube having increased conductivity, during movement of said selector and the movable member out of coincidence, storing a counter signal potential corresponding to the resultant relative displacement of said transmitter and receiver; such counter signal potential, during movement of the movable member and said selector toward coincidence, being impressed on anode and control grid of the associated tube in a direction to oppose the signal voltage impressed on the control grid thereof; and said impedances, during such latter movement, dissipating such counter signal potential at a rate less than the decrease in such signal voltage responsive to such movement, whereby such counter signal potential exceeds such signal voltage when the member and said selector approach coincidence to shift such null zone in a direction to decrease the conductivity of the associated tube to equalize the conductivity of said tubes and thus effect opera tion of said relay armature to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence,

' whereby to inhibit relative hunting thereof; the

effective signal voltage on the control grid of the other tube reaching a value insufllcient to condition said tubes to effect deenergization of said motor only when the movable member and said selector have attained substantially full concidence; and a second anti-hunting null shifting circuit arrangement comprising circuit means individual to each tube and operative upon operation of said differential relay to reduce the operating potential applied from such reference source to the associated tube to shift the null zone in a direction to condition said tubes to operate said relay to deenergize said motor and disconnect it from said actuator before the member and said selector attain coincidence, whereby to inhibit REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,942,587 Whitman Jan. 9, 1934 2,154,375 Chambers Apr. 11, 1939 2,287,002 Moseley June 16, 1942 2,085,442 Newell June 29, 1937 

